1. Field of the Invention
This invention relates to a dehydrocyclization process for converting C8 isoalkanes and C8 isoalkenes to para-xylene.
2. Prior Art
Para-xylene (PX) is a valuable basic chemicals useful in chemical industry. Commercial xylenes generally comprise three aromatic isomers, inclusive of PX, and may be produced by reforming hydrocarbon feedstocks rich in naphthenes or by dehydrocyclization of naphtha feedstocks, which are rich in C6 to C20 paraffins, or olefins.
For example, U.S. Pat. No. 3,449,461 discloses the production of mixed xylenes and other aromatics by subjecting a paraffinic feed to dehydrocyclization conditions over a sulfided refractory oxide catalyst containing a noble metal such as platinum. In accordance with U.S. Pat. No. 3,766,291, feedstock comprising 3-methylbutene-1 is converted to PX by disproportionation to 2,5-dimethylhexene which is subsequently dehydrocyclized over a catalyst containing at least one Group VIII metal associated with tin in combination with a Group II aluminate spinel support material.
U.S. Pat. No. 3,428,702 discloses the dehydrocyclization of 2,5-dimethylhexene in the presence of H2S using a chromia-alumina catalyst such that 30-40% of the 2,5-dimethylhexene is converted to PX. Other dehydrocyclization processes for converting aliphatic or olefinic hydrocarbons to xylenes are found in U.S. Pat. No. 3,207,801, wherein catalysts based on magnesium oxide, hydoxide or magnesium acid salts are used, and in U.S. Pat. No. 4,910,357 wherein a platinum-loaded, non-acidic, metal modified zeolite support such as ZSM-5 is used.
While these and other methods for the production of xylenes are effective and useful, there is a continuing need in the art to provide a process which is highly selective for producing PX and in high yields from hydrocarbon feedstocks containing less valuable alkane and alkene compounds.